A continuous motion saw is designed to cut a product in motion. Illustrative products are "logs" of bathroom tissue and kitchen toweling. The invention, however, is not limited to such products but can be used to advantage on other multi-ply products, such as bolts of facial tissue, interfolded or otherwise.
The illustrative products, for example, are produced at high speed on machines termed "rewinders". These machines start with a parent roll perhaps 10 feet long and 8 feet in diameter--resulting from the output of a paper-making machine. The parent roll is unwound to provide a web which is usually transversely perforated (in the U.S. on 41/2" centers for bathroom tissue and 11" centers for kitchen toweling and then rewound into retail size rolls of 4"-8" in diameter. Conventional high speed automatic rewinders can produce upwards of 30 logs per minute. These logs then are delivered to a log saw where they are moved axially for severing into retail size lengths--again normally 41/2" for bathroom tissue and 11" for kitchen toweling. This results in the well-known "squares" of tissue and toweling.
To have a saw capable of keeping up with high speed rewinders it is necessary to cut the log while it is in motion. To achieve a "square" cut on the moving log, the blade must have a cutting motion perpendicular to the log while also having a matched component of motion parallel of the log travel. To produce this combined motion, the orbit centerline of the blade is "skewed" with respect to the log center line. This skew angle is increased for "Long cut" lengths and is decreased for "short cut" lengths.
Even though the saw head is mounted at this skewed angle, the blades must always remain perpendicular to the log to provide a square cut. This required that the blades be mounted on an angled housing (equal and opposite to the skew angle) and driven by a 1:1 planetary motion to maintain their perpendicular relation to the log as the main arm rotates.
It was also necessary to maintain a razor-like sharpness on the cutting edge of the blades. To do this, the grinding system must be mounted on the angled housings and follow the planetary motion. Because the grinders are mounted out on the blade's edge, each blade/grinder assembly is difficult to balance, especially due to the changing position of the grinders as the blade diameter decreases. Since the system was generally out of balance, the planetary gear train had to deal with the constant imbalance torque and its cyclic nature, reversing once each revolution. The planetary motion also put the grinder into completely reversing cyclic loading causing component fatigue and grind quality problems as production speed requirement increased.
Problems were also associated with changing the skew angle to produce various product lengths. After changing the framework of the saw to a new skew angle, the blade mounting and drive components had to be replaced. The angled block mounting the blade had to be changed to return the blades back to perpendicular and the bevel gears inside it that were used to drive blades had to be changed to continue to match the angled housing.
These all combined to produce a complex cutterhead assembly that make changing skew angles an involved and time-consuming process. This system has also proven to be complex causing high maintenance due to a complex blade drive and blade orienting planetary system. The design was also speed limiting due to the planetary motion of the grinders causing cyclic loading and the requirement that the grinders follow the same orbit radius of movement as the blades, causing them to have to withstand full centrifugal loading
The problem, therefore, was to produce this same type of blade action but without the use of planetary motion. For this, the invention provides a motion that allows for locating of the grinders at a lesser orbit radius than the blade center and leaves them always toward the center of rotation, thereby eliminating the cyclic centrifugal forces. At the same time, the invention provides the ability to change the skew angle quickly, even automatically, with no change parts.
According to the invention in the specific embodiment illustrated, the blade, blade drive motor, and grinding stone assemblies are mounted on the same mounting pivot bracket. One bracket is mounted on each end of a rotating drive arm. Directly behind the arm is a control arm linkage connecting the two brackets from behind. The linkage, which has tie rod characteristics, is mounted off-center to the orbit head assembly center of rotation causing the blade and grinding stone mounting pivot brackets to oscillate back and forth as the arm rotates. This action allows the blades to follow an eccentric pattern with respect to the axis of rotation to keep them perpendicular with the log or folded web. The entire orbit head assembly is mounted skewed with respect to the log or folded web. The amount of eccentricity is dependent on the skew angle of the orbit head assembly and the skew angle is dependent on the linear speed of the log or folded web in order to achieve the desired square cut-off. The movable eccentric in this invention is also advantageous to bring the blades back to perpendicular as the skew angle changes correcting for changes of head skew. The amount of head skew is regulated through the use of two skew adjustment linkages that the orbit head assembly is mounted on. It could be done manually or automatically with sensors and drive motors which would allow changing the rate of feed of the log or folded web on the fly.
In principle, the inventive continuous motion saw and method includes a frame providing a linear path or elongated web plies and conveyor means operatively associated with the frame for advancing the elongated web plies along the linear path. The frame also has a blade-equipped drive arm rotatably mounted thereon with means for rotating the drive arm about an axis skewed with respect to the linear path. A bracket is connected adjacent an end of the drive arm for two degrees of pivotal movement, the bracket or brackets also carrying the blade or blades. Means are provided on the bracket for rotating the blades. Thus, rotation of the blade arm orbits the blade or blades and the orbit resulting therefrom intersects the path. The invention further includes a control arm rotatably mounted on the frame adjacent the blade arm for rotation about an axis eccentric to the blade arm axis. The control arm adjacent the end or ends thereof is connected to the bracket or brackets again for two degrees of pivotal freedom so that rotation of both of the arms orients the blade or blades perpendicular to the linear path. This eliminates the planetary motion of the prior art and allows for the grinding stone assemblies to remain close to the center of rotation of the cutter head assembly-- thereby reducing the centrifugal forces of the system and eliminating the cyclic nature of the force, thereby allowing for greater speeds. The new simplified construction which has the motor, blade and grinding assembly all attached to one pivot bracket and connected to a drive and control arm offers a more user-friendly system with fewer parts, lower cost, less maintenance, greater speeds and more versatility.
The invention is described in conjunction with an illustrative embodiment in the accompanying drawing.